Alpha-crystallin, isolated from calf lenses by Sephacryl S-200 Superfine, was strongly blue-fluorescent, exhibiting a double-peaked fluorescence spectrum (double-peaked alpha-crystallin). When deaggregated, its fluorescence became single-peaked and weak, as shown in weakly blue-fluorescent alpha-crystallin isolated by Sephadex G-200 (single peaked alpha-crystallin). This highly aggregated protein appears to exist in different aggregated forms with varied optical properties. Upon aging, in the nuclear region of bovine lenses, blue-fluorescent low-molecular weight alpha-crystallin shifted to non-covalently linked high molecular weight aggregates which were also blue-fluorescent. The nucleus of adult bovine lenses also contained blue-fluorescent water-insoluble proteins. New photochemical and fluorescent reactions were found in blue-fluorescent calf lens alpha-crystallin. Exposure of single-peaked alpha-crystallin to 300 nm - UV light increased blue fluorescence. When this photochemically produced blue-fluorescent alpha-crystallin was irradiated subsequently wth 365 nm - UV light, it underwent further photochemical reactions, giving rise to new blue fluorescences. The blue fluorescence of double-peaked alpha-crystallin disappeared gradually with 365 nm - UV irradiation, but was partially regenerated by 300 nm -UV light.